Method of manufacturing wires consisting at least superficially of boron and wires obtained by said method

ABSTRACT

To enhance the tensile strength, boron-coated tungsten wire may be etched with an etchant comprising phosphoric acid, nitric acid and water.

Vrieze et al.

METHOD OF MANUFACTURING WIRES CONSISTING AT LEAST SUPERFICIALLY OF BORON AND WIRES OBTAINED BY SAID METHOD Inventors: Wubbe Vrieze; Otmar Schob, both of Emmasingel, Eindhoven,

Appl. No.: 190,378

Foreign Application Priority Data Oct. 2], i970 Netherlands 7015375 1 Jan. 15, 1974 [52] US. Cl 156/3, 156/2, 252/792 [5|] Int. Cl. C23f 17/00 [58] Field of Search 156/2, 3; 252/792 [56] References Cited UNITED STATES PATENTS 2,879,147 3/l959 Baker 156/24 3,446,682 5/I969 Wawner 156/3 Primary Examiner-Jacob H. Steinberg AttorneyFrank R. Trifari [57] ABSTRACT To enhance the tensile strength, boron-coated tungsten wire may be etched with an etchant comprising phosphoric acid, nitric acid and water.

3 Claims, No Drawings METHOD OF MANUFACTURING WIRES CONSISTING AT LEAST SUPERFICIALLY OF BORON AND WIRES OBTAINED BY SAID METHOD The invention relates to a method of manufacturing wires which at least at their surface consists of boron, in which boron is deposited on a support and in which a part of the boron surface is subsequently etched off by means of an etchant comprising nitric acid.

Such a method is known, for example, from U.S. Pat. No. 3,446,682.

The purpose of etching offa part of the boron surface is to remove surface errors which have a detrimental influence on the mechanical properties of the wires and to enhance, inter alia, the tensile strength of the wires.

In Boron vol. 2, edition GK. Gaule, pages 283 to 300 (The effect of ChemicalPolishing on the Strength and Fracture Characteristics of Amorphous Boron Filaments" by F.E. Wawner Jr.) it has been stated that optimum results can be achieved with mixtures of concentrated nitric acid and water in a volume ratio of 1:1. The etching rate is then approximately 2.5 micrometres per minute at a temperature of 100C the etchant. Less satisfactory results are obtained with other ratios, with mixtures of sulphuric acid and nitric acid and with potassium periodate solutions. In practice, however, it was found that highly varying results may be obtained when using mixtures of concentrates nitric acid and water in a ratio of 1:1. In some wires the mean etching rate is more than approximately 2.5 micrometres per minute, particularly when etching takes place over a comparatively long period. In other wires hardly anything is etched off during exposure to the etchant.

This can only be explained when it is assumed that very pure crystallized boron is coated with an oxide layer protecting against attack by the etchant during etching with an etchant having an oxidising effect.

The etching rate is then especially determined by the density of the boron oxide layer, by the rate at which these oxides dissolve in the etchant and by the presence or absence of impurities.

An object of the present invention is to provide a method by which wires of great strength are also obtained, but in which etching off proceeds in a reliable and regular manner.

According to the invention such a method is characterized in that the boron surface is etched off with an etchant containing 55 to 85 percent by weight of H PO 2 to 20 percent by weight of HNO and to 35 by weight of water.

It was found that optimum results are obtained when the temperature of the etchant is approximately 100C.

When using the said etchants, the etching rate is at least approximately 2.5 micrometres per minute. The advantage of these etchants as compared with the use of nitric acid as an etchant is that this rate is immediately achieved for all wires and that, consequently, there is no run-in period. This means that after the etching rate of a bath is determined, any desired decrease in diameter may be obtained by etching the wires over a predetermined period.

Etching rates of approximately 4.5 micrometres per minute and more may be obtained with etchants which contain from 70 to 85 percent by weight of H PO. 2

to 15 percent by weight of HNO and 10 to 25 percent by weight of water.

In order that the invention may be readily carried into effect, it will now be described with reference to several examples.

EXAMPLE I An etching bath of the following composition was prepared 78.1 by weight of H PO 4.9 by weight of I-INO 17.0 by weight of H 0 by mixing 10 parts by volume of concentrated HNO (60 percent by weight of I-INO in water) with parts by volume of H PO (85 percent by weight of H PO in water). The etching rate was determined on wires having a diameter of 96 micrometres which had been obtained as follows:

A tungsten wire having a diameter of 12.5 micrometres was passed at a constant rate through a space through which gaseous boron trichloride and hydrogen in a mixture ratio of 1:3 was passed.

The tungsten wire was heated by a direct current passage at a temperature of approximately 1,100C.

The etching-off rates were determined by etching wire pieces with the etchant (temperature C).

The results mentioned in Table I were obtained.

TABLE I Wire diameter etching rate in p.m per min.

etching time prior to after in minutes etching etching in am in um EXAMPLE 11 As in Example I, 5 wires having a diameter of 97 um were etched for one minute. The average tensile strength prior to etching was 229 kglsqmm, after etching it was 297 kg/sqmm, which is an increase of the average tensile strength by approximately 30 percent.

EXAMPLE III EXAMPLE IV The etchant according to Example 1 was compared with an etchant consisting of 42.5 percent by weight'of HNO obtained by mixing 64 parts by volume of concentrated I-INO with 36 parts by volume of water. Then the results according to Table II were obtained.

TABLE II Etchant according to 42.5% by weight of HNO aq Example I diameter etching after tensile diameter tensile time in etching strength after etstrength in minutes in pm kg/sq.mm. ching in pm kglsq.mm.

A B A B 96 301 29l 96 30l 29l l 83 316 342 90 308 304 2 73 336 294 85 305 287 3 65 320 308 80 293 28l 4 57 241 229 62 233 24l 5 50 190 202 55 NH 98 A tensile length l0 cm B tensile length l cm.

Table ll shows that with the etchant according to Example l, starting from the same average tensile strength level prior to etching for a comparable decrease in diameter, always higher values of the average tensile strength are obtained than with an etchant comprising nitric acid only.

What is claimed is:

l. A method of improving the physical properties of a boron wire produced by deposition of a gaseous mixture comprising a volatile boron compound on a hot substrate comprising, etching the resultant boron surface with an etchant comprising 55 to 85 percent by weight of H POg, 2 to percent by weight of HNO and 10 to 35 percent by weight of water at a rate of at least about 2.5 micrometres per minute and at -a temperature sufficiently high to remove surface errors from the boron surface.

2. A method as claimed in claim 1, characterized in that the etchant is used at a temperature of approximately 100C.

3. A method as claimed in claim 1, characterized in that the boron surface is etched off with an etchant comprising to percent by weight of H PO 2 to 15 percent by weight of HNO; and 10 to 25 percent by weight of water. 

2. A method as claimed in claim 1, characterized in that the etchant is used at a temperature of approximately 100*C.
 3. A method as claimed in claim 1, characterized in that the boron surface is etched off with an etchant comprising 70 to 85 percent by weight of H3PO4, 2 to 15 percent by weight of HNO3 and 10 to 25 percent by weight of water. 